Solid oxide electrolyte fuel cell

ABSTRACT

A planar type solid oxide electrolyte fuel cell which is composed of power generation films in which an oxygen electrode is constituted on one side of each solid electrolyte having dimples almost all over its surface and a fuel electrode on the other side thereof, interconnectors sandwiched between the said power generation films, and seal materials which surround the four sides of the said power generation films, wherein oxidant gases and fuel gases react electrochemically via the said power generation films in order to obtain electric energy, wherein on the fuel electrode side of one the four sides of the cell a fuel inlet aperture is provided over nearly the entire length thereof, and a fuel outlet aperture is provided on the side facing the said one side over nearly the entire length thereof, and an air inlet aperture is provided on the oxygen electrode side of one of the remaining two sides, the said air inlet aperture being located in that half of the said side which is closer to the fuel gas inlet aperture, and an air outlet aperture is provided on the side facing the said air inlet aperture, the said air outlet aperture being located in about that half the said side which is closer to the fuel outlet aperture.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/JP98/05104 which has an Internationalfiling date of Nov. 13, 1998, which designated the United States ofAmerica.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a compact and economical solid oxideelectrolyte fuel cell which comprises a simple structure to provide alarge power generation area, and the thermal stress generated therein islow to ensure reliable fuel cell characteristics.

2. Background Technology

Conventionally, as a planar type solid oxide electrolyte fuel cell(hereinafter SOFC) in which power generation films comprise a dimpledstructure (hereinafter “dimples”), the configuration shown in FIGS. 15and 16 is known.

FIG. 15 is an exploded perspective view of the SOFC and FIG. 16 is asectional view taken along line X—X in FIG. 15. In these figures,reference numeral 1 denotes an interconnector (also called a gasseparator); 2, a power generation film, which together with theinterconnector 1 constitute a unified fuel cell structure 10(hereinafter “stack”) in such a manner that from top to bottom aninterconnector 1, a power generation film 2, an interconnector 1, and soon, are alternately superposed.

The power generation film 2 is the smallest unit cell (also called acell) that constitutes a SDFC, and is mainly composed of a solidelectrolyte film 20 comprising convex dimples 21 and concave dimples 22substantially all over its surfaces, an oxygen electrode 23 on one sideof the solid electrolyte film 20, and a fuel electrode 24 on the otherside thereof.

In the SOFC shown in FIGS. 15 and 16, the side having convex dimples 21is the oxygen electrode 23 and the side having concave dimples serves asthe fuel electrode 24. The above power generation film 2 is surroundedby a seal material 3 in the circumference thereof, except for gas inletand outlet apertures through which oxidant gases (e.g. air, hereinafterair) and fuel gases pass, and each film is sandwiched between twointerconnectors 1 to form air flow passages 41 and fuel gas flowpassages 42.

The above interconnectors 1, on the other hand, are connected with theseal material 3 to provide space between themselves and the adjacentpower generation film 2 and constitute gas flow passages, whileproviding electrical functions for series connection by contacting orconnecting with the dimple protrusions of the adjacent power generationfilms.

The SOFC stack 10 thus constituted is then kept in a high temperaturerange of 800° C.˜1000° C., and power is generated when air flows throughthe air passages 41 and a fuel gas through the gas passages 42,respectively, as illustrated in FIGS. 15 and 16.

In the example in FIG. 15, the air flow and the fuel gas flow areperpendicular to each other on the top and the bottom side of each powergeneration film 2. For this reason, a SOFC having this kind of gas flowlayout is generally called a cross flow type.

In the cross flow type shown in FIG. 15, an air inlet 43 is provided onone of the four sides of each planar type cell and an air outlet 44 isconstituted on the opposite side thereof, whereas a fuel gas inlet 45 isgiven on one of the remaining sides and a fuel outlet (not shown) isprepared on the facing side thereof.

On the other hand, there is a planar cross flow type SOFC, in which eachpower generation film 2 is a flat plate without any dimple and groovesare provided in the interconectors 1 to constitute gas flow passages. Atypical example of this configuration is shown in FIGS. 17 and 18.

FIG. 17 is an exploded perspective view of the said SOFC; FIGS. 18(a)and 18(b) are sectional views taken along line X—X and line Y—Y in FIG.17, respectively

Each power generation film 2 is a flat plate without any dimple, and iscomposed of a solid electrolyte film 20, an oxygen electrode 23 on oneside of the power generation film 20, and a fuel electrode 24 on theother side thereof in FIG. 18.

In FIG. 17, reference numeral 1 denotes an intermediate interconnectoron both sides of which multiple rows of grooves 33 for gas flow areprovided along the direction of gas flow. Reference numerals 1 c and 1 din the same figure indicate an upper interconnector and a lowerinterconnector of the stack 11, respectively. On the surface facing apower generation film 2 of each of these interconnectors, multiplegrooves 33 are provided along the direction of gas flow, and theopposite surface thereof is usually flat to fit power collecting partsfor taking out electric current. The interconnectors 1, the upperinterconnector 1 c, and the lower interconnector 1 d alternately isolatethe power generation films 2, thereby forming air flow passages 41 andfuel gas flow passages 42 between themselves and the adjacent powergeneration films 2, and having at the same time functions for electricalseries connection by contacting or connecting with the protrusions 32 ofthe interconnectors and the oxygen electrodes 23 as well as the fuelelectrodes 24 of the adjacent power generation films.

In FIG. 17, the SOFC stack 11 is composed of an upper interconnctor 1 c,a power generation film 2, an intermediate interconnctor 1, a powergeneration film 2, . . . , a lower interconnector 1 d, which aresuperposed alternately from top to bottom, thus constituting a unifiedstructure. The stack 11 is then kept in a temperature range of 800°C.˜1000° C., and power is generated, as shown in FIG. 18, by letting airflow through the air flow passages 41 and a fuel gas through the fuelgas flow passages 42.

In a SOFC, the operation temperature is as high as 800° C.˜1000° C., andthe reaction in the fuel cell generates heat. As a result, thetemperature distribution in the fuel cell is such that the area near thegas inlet is in a low temperature range and the area near the gas outletis in a high temperature range. In the SOFC's as shown in FIGS. 15˜18 inwhich the gas flow occurs according to the cross flow method, atemperature distribution as shown in FIG. 20(a) is observed. The %values in FIG. 20(a) indicate approximate ratios when the temperaturedifference between the gas inlet and the gas outlet is regarded as 100%.Once such a temperature distribution occurs, thermal stress is generatedin each part of the fuel cell. If the thermal stress becomes too high,the heat build-up associated with the cell reaction increases by takingout much output, for example, and an excessive temperature differencebetween the gas inlet and the gas outlet results in a higher thermalstress, thus causing the electrical connection between the stacked cellsto deteriorate partially, or damaging the surrounding gas seal parts tocause a decrease in power generation capability, which in some casescould lead to fractures of the interconnectors or the power generationfilms. In such cases, the expected power output cannot be obtained andthe function as a fuel cell itself may be lost.

One of the means to avoid such trouble is to decrease the temperaturedifference between the gas inlet and the gas outlet of the fuel cell byproviding much air to remove the reaction heat of the cell, thusmaintaining reliable characteristics of the fuel cell.

However, such a method requires high ventilating power to send a largevolume of air, as well as a large-sized heat exchanger or heater inorder to preheat the large volume of air up to a temperature close tothe operating temperature of the SOFC. As a result, the fuel cellbecomes uneconomical as a power generation unit.

On the other hand, as a structural means to solve the above problem,there is the so-called co-flow method by which the air and the fuel gasflow parallel to each other in the same direction.

A typical example which employs this method is shown in FIGS. 21 and 22.In these figures, reference numeral 5 denotes a header; 6, a gaspre-flow rectifying section. Both 5 and 6 are provided as rectifyingsections for the air or the fuel gas to flow uniformly in one direction.The other reference numerals are the same as those explained in FIGS.15, 16 and 17, 18.

In the SOFC illustrated in FIGS. 21 and 22, in which the co-flow methodis employed, a temperature distribution as shown in FIG. 20(b) isobserved. In such a fuel cell, the temperature increases gradually from-he gas inlet toward the gas outlet of the cell, enabling relativelyfree thermal expansion with small self-constraint. As a result, thethermal stress caused by the heat build-up in the cell becomes alsosmall. In summary, under the same condition, the heat distribution thatoccurs in the cell of the co-flow type shown in FIG. 20(b) results inlower thermal stress than in the cell of the cross flow type in FIG.20(a), thus improving the fuel cell characteristics and providing fullperformance of the fuel cell.

By the co-flow method, however, it is necessary to prepare two kinds ofgas inlet apertures 43, 45 for air and fuel gases, respectively, oroutlet apertures 44, 64 on one of the four sides of the planar fuelcell, which requires a more complicated manifold structure for gas inletand outlet. As a result, the co-flow method becomes inferior to thecross flow method in terms of reliability and economy.

In order to obtain the temperature distribution as shown in FIG. 20(b),it is also necessary to let the gases flow uniformly in one direction.To realize this goal, the header 5 as shown in FIG. 21 or the gaspre-flow rectifying section 6 as shown in FIG. 22 has been invented. Fora uniform gas flow, the header (reference numeral 5 in FIG. 21) and thegas pre-flow rectifying section (reference numeral 6 in FIG. 22) need tobe wide enough, which does not actually contribute to the powergeneration itself, resulting in a relative decrease in the effectivepower generation area of the fuel cell (i.e. in the power generationfilm in FIGS. 21 or 22, the area contributing to the power generation isonly the hatched part that comprises the oxygen electrode 23 on one sideand the fuel electrode 24 on the other side). As a result, the fuel cellbecomes larger in order to obtain a desired power output, and lesseconomical as compared with the cross flow method.

As explained above, by -he cross flow method, each of the air flow andthe fuel gas flow are almost uniform in one direction, and the cellreaction is efficient by using nearly the entire surface of the powergeneration film, whereas high thermal stress occurs, which may lead tounreliable cell characteristics. By the co-flow method, on the otherhand, less thermal stress occurs, and therefore better cellcharacteristics can be obtained as compared with the cross flow method.However, a header or a gas pre-flow rectifying section which does notcontribute to power generation becomes necessary in order to realize anideally uniform parallel gas flow in one direction for a sufficient cellperformance, thus inevitably requiring a larger fuel cell area to obtaina desired power output, which makes the co-flow method less economical.For this reason, required is a fuel cell structure which compensates thedisadvantages of both of the above-mentioned gas flow methods.

In view of the above problems, an object of the present invention is toprovide a compact and economical SOFC in which the thermal stress is lowto realize reliable cell characteristics and the structure is simple toensure a wide power generation area as is the case with a SOFC by thecross flow method.

DISCLOSURE OF THE INVENTION

The first claim of the present invention that attains the above objectis realized in a planar type SOFC which comprises a power generationfilm or a plurality of power generation films, each having an oxygenelectrode on one side and a fuel electrode on the other side thereof,interconnectors sandwiching the said power generation film(s), and aseal material surrounding the four sides of the said power generationfilm(s), wherein electric energy is obtained by reacting an oxidant gaswith a fuel gas electrochemically via the said power generation film(s).In the said SOFC, a fuel gas inlet aperture is provided over nearly theentire length of one of the four sides of each cell, the said side beingon the fuel electrode side of the cell, and a fuel outlet aperture isprovided over nearly the entire length of the opposite side thereof,whereas an air inlet aperture is provided on one of the remaining twosides thereof, the said air inlet aperture being located on the oxygenelectrode side and in that half of the side which is closer to the gasoutlet aperture, and an air outlet aperture is provided on the sidefacing the said air inlet aperture, the said air outlet aperture beinglocated in that half of the said side which is closer to the fuel gasoutlet aperture.

Such an embodiment provides a compact and economical SOFC in which thethermal stress is low to realize reliable cell characteristics and thestructure is simple to ensure a large power generation area.

The second claim of the present invention is a planar type SOFC as inthe first claim, wherein each of the said power generation films is asolid electrolyte which comprises dimples over nearly the entire surfacethereof, having an oxygen electrode on one side and a fuel electrode onthe other side thereof.

The third claim of the present invention is a planar type SOFC as in thesecond claim, wherein the air inlet aperture constitutes a cell on theright side of the fuel gas inlet aperture and another cell on the leftside thereof, the said cells being superposed alternately viainterconnectors for electrical series connection in a unified structure.

The fourth claim is a planar type FOFC as in the second claim of theinvention, which comprises multiple layers of said interconnectors andsaid power generation films arranged next to one another, wherein thefuel gas outlet aperture faces upwards and the fuel gas inlet aperturefaces downwards.

The fifth claim is a planar type SOFC as in the second claim, whereinthe said fuel gas side and the said air side are replaced completelywith each other.

The sixth claim is a planar type SOFC as in the first claim, whereineach of the said power generation films is a rectangular planar solidelectrolyte which comprises a fuel electrode on one side and an oxygenelectrode on the other side thereof, and grooves for gas flow areprovided on both sides of each interconnector so that fuel gases oroxidant gases can be supplied to each electrode side of the adjacentpower generation films, whereas the four surrounding sides of eachinterconnector, except the gas inlet and the gas outlet, comprise aflat-surfaced support frame to support the adjacent power generationfilm(s) as well as to insulate gases, and a fuel gas and air reactelectrochemically via the said power generation films in order to takeout electrical energy.

The seventh claim is a planar type SOFC as in the sixth claim of theinvention, wherein the air inlet aperture forms a cell located on theright side of the fuel gas inlet aperture and another cell situated onthe left side thereof, and the interconnectors and the power generationfilms are superposed alternately for electrical series connection in aunified structure.

The eighth claim is a planar type SOFC as in the sixth claim, whereinthe said interconnectors and the said power generation films aresuperposed in such a manner that the fuel gas outlet faces upwards andthe fuel gas inlet faces downwards.

The ninth claim is a planar type FCFC as in the sixth claim of theinvention, wherein the said gas fuel side and the said air side arereplaced completely with each other.

The tenth claim is a planar type SOFC as in the second or the sixthclaim of the invention, wherein the entire gas supply manifold or a partthereof is constituted as an internal manifold system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing a planar type SOFCaccording to the first embodiment of the present invention;

FIG. 2 is a sectional view along line X—X in FIG. 1;

FIG. 3(c) is a schematic front view of the power generation film 2 a ofthe first embodiment, FIG. 3(a) is a cross-sectional view of the film 2a taken along line X—X in FIG. 3(c), FIG. 3(b) is a right side view ofthe film 2 a, and FIG. 3(d) is a cross-sectional view of the file 2 ataken along line Y—Y in FIG. 3(c);

FIG. 4(c) is a schematic front view of the power generation film 2 b ofthe first embodiment, FIG. 4(a) is a cross-sectional view of the film 2b taken along line X—X in FIG. 4(c), FIG. 4(b) is a left side view ofthe film 2 b, and FIG. 4(d) is a cross-sectional view of the file 2 btaken along line Y—Y in FIG. 4(c);

FIG. 5 is a perspective view showing a vertically placed SOFC in whichmanifolds for gas supply and discharge are attached to the unified fuelcell structure comprising a plurality of unit cells superposed upon oneanother;

FIG. 6 is a perspective view showing a horizontally placed SOFC in whichmanifolds for gas supply and outlet are attached to the unified fuelcell structure comprising a plurality of unit cells superposed upon oneanother;

FIG. 7 is an exploded perspective view showing a planar type SOFCaccording to the second embodiment of the present invention;

FIG. 8(a) is a sectional view taken along line X—X, and FIG. 8(b) is asectional view taken along line Y—Y in FIG. 7, respectively;

FIG. 9(c) is a schematic front view of the intermediate interconnector 1a in the second embodiment, FIG. 9(a) is a cross-sectional view of theinterconnector 1 a taken along line X—X in FIG. 9(c), FIG. 9(b) is aright side view of the interconnector 1 a, and FIG. 9(d) is across-sectional view of the interconnector 1 a taken along line Y—Y inFIG. 9(c);

FIG. 10(c) is a schematic front view of the interconnector 1 b in thesecond embodiment, FIG. 10(a) is a cross-sectional view of theinterconnector 1 b taken along line X—X in FIG. 10(c), FIG. 10(b) is aright side view of the interconnector 1 b, and FIG. 10(d) is across-sectional view of the interconnector 1 b taken along line Y—Y inFIG. 10(c);

FIG. 11; is an exploded perspective view showing a planar type SOFCcomprising internal manifolds according to the third.

FIG. 12 is a sectional view taken along line X—X in FIG. 11;

FIG. 13(b) is a schematic front view of the power generation film 2 a inthe third embodiment, FIG. 13(a) is a cross-sectional view of the film 2a taken along line X—X in FIG. 13(b), and FIG. 13(c) is across-sectional view of the film 2 a taken along line Y—Y in FIG. 13(c);

FIG. 14(b) is a schematic front view of the power generation film 2 b inthe second embodiment, FIG. 10(a) is a cross-sectional view of the film2 b taken along line X—X in FIG. 14(b), and FIG. 14(c) is across-sectional view of the film 2 b taken along line Y—Y in FIG. 14(b);

FIG. 15; is an exploded perspective view showing a solid oxideelectrolyte fuel cell (SOFC) comprising dimples to provide gas flowpassages according to the earlier technology;

FIG. 16 is a sectional view taken along line X—X in FIG. 15;

FIG. 17 is an exploded perspective view showing a SOFC in which groovesare provided in interconnectors to form gas flow passages;

FIG. 18(a) is a sectional view taken along line X—X, and FIG. 18(b) is asectional view taken along line Y—Y in FIG. 17, respectively;

FIGS. 19(a), 19(b), and 19(c) show isothermal diagrams of the unit cellof a power generation film;

FIGS. 20(a) and 20(b) show isothermal diagrams of the unit cell of apower generation film;

FIG. 21(b) is a schematic front view of a SOFC comprising a headeraccording to the co-flow method, FIG. 21(a) is a cross-sectional viewtaken along line X—X in FIG. 21(b) and shows an air flow therein, andFIG. 21(c) is a cross-sectional view taken along line Y—Y in FIG. 21(c)and shows a fuel gas flow therein;

FIG. 22(b) is a schematic front view of a SOFC comprising gas pre-flowrectifying sections according to the co-flow method, FIG. 22(a) is across-sectional view taken along line X—X in FIG. 22(b) and shows an airflow therein, and FIG. 22(c) is a cross-sectional view taken along lineY—Y in FIG. 22(b) and shows a fuel gas flow therein;

FIG. 23 is a simplified perspective view of a SOFC comprising substacksin the fourth embodiment of the present invention;

FIG. 24(a) a simplified view of a first air chamber in the fourthembodiment, and FIG. 24(b) is a simplified view of a second air chamberin the same embodiment; and

FIG. 25(a) is simplified view of a third air chamber in the fourthembodiment, and FIG. 25(b) shows a configuration of air inlet aperturesand an outlet apertures.

BEST MODE FOR CARRYING CUT THE INVENTION

In order to explain the present invention in more detail, preferredembodiments will be hereinafter described with reference to theaccompanying drawings, which in no way limit the invention.

[Embodiment 1]

FIGS. 1 is an exploded perspective view of the planar type solidelectrolyte fuel cell (hereinafter SOFC) in the first embodiment of theinvention. FIG. 2 is a sectional view taken along line X—X in FIG. 1.FIGS. 3, 4 are schematic views, each consisting of a side view and asectional view, showing two different kinds of unit cells (powergeneration films 2 a, 2 b). FIGS. 5 and 6 are perspective views ofSOFC's in which manifolds for gas inlet and gas outlet are provided in aunified cell structure comprising multiple layers of unit cellsaccording to the present invention.

In the first embodiment, the present invention is applied to a SOFC inwhich the power generation films comprise dimples as shown in FIGS. 15and 16 explained in the earlier technology. The planar SOFC according tothe first embodiment of the invention will be described with referenceto FIG. 1 (exploded perspective view) and FIG. 2 (sectional view takenalong line X—X in FIG. 1).

Reference numerals 2 a and 2 b in FIG. 1 denote power generation films,each of which is composed of a solid electrolyte film 20 comprisingconvex dimples 21 and concave dimples 22 almost all over the surfacethereof, and the said electrolyte film having an oxygen electrode 23 onone side and a fuel electrode 24 on the other side thereof.

In FIGS. 1 and 2, the top side of the convex dimples 21 is the oxygenelectrode 23, and the back side of the concave dimples 22 the fuelelectrode 24, respectively.

The power generation films 2 a and 2 b are surrounded, except for theinlet and the outlet apertures through which gases pass through, by theseal material 3, thereby forming the air flow passages 41 and the fuelgas flow passages 42 which are each sandwiched between one powergeneration film and the adjacent interconnector 1 as illustrated in FIG.2.

The power generation film 2 a and the power generation film 2 b havedifferent air flow passages, which are shown in FIGS. 3 and 4 by usingtheir respective side views and sectional views taken along lines X—Xand Y—Y. In these figures, the middle part of the top side of the powergeneration films 2 a and 2 b is the oxygen electrode 23, and the backside is the fuel electrode 24, with the solid electrolyte film 20sandwiched between both electrodes.

The part constituted by the electrodes 23 and 24 is the area in whichcell reactions take place, and is generally called the effective powergeneration part, the surface area thereof being the effective powergeneration area.

Numeral 45 in FIG. 3 denotes a fuel gas inlet aperture which is openover nearly the entire length of one of the four sides on the fuelelectrode side of the power generation films 2 a and 2 b, and numeral 46referring to a fuel gas outlet aperture which is open over nearly theentire length of the opposite side of the fuel inlet aperture 45, withthe remaining sides being surrounded by the seal material 3.

Reference numerals 43 a, 43 b in FIGS. 3 and 4 denote air inletapertures; 44 a and 44 b, air outlet apertures, respectively. The airinlet apertures 43 a, 43 b and the air outlet apertures 44 a, 44 b areprovided on one of the other two sides of the rectangular powergeneration film, on which neither the fuel gas inlet aperture 45 nor thefuel gas outlet aperture 46 is provided. The air inlet apertures 43 a,43 b are provided in approximately that half of the said side which iscloser to the gas inlet aperture 45, and the air outlet apertures 44 a,44 b in approximately that half of the side which is closer to the fuelgas outlet aperture 46.

The part of the four sides other than the apertures is surrounded by theseal material 3, which means that, in the power generation film 2 asshown in the sectional view taken along line X—X in FIG. 3, the air issurrounded by the seal material 3 so as to enter from the air inletaperture 43 a situated in the lower right side in FIG. 3(a), and isguided to the air outlet aperture 44 a situated on the upper left sidetherein.

Similarly, in the power generation film 2 b shown in the sectional viewtaken along line X—X in FIG. 4, the air is surrounded by the sealmaterial 3 so as to enter from the air inlet aperture 43 b situated onthe lower left side in FIG. 4(a), and is guided to the air outletaperture 44 b situated on the upper right side therein.

On the other hand, on the side of the fuel electrode 24 in the powergeneration films 2 a and 2 b shown in the sectional views taken alongline Y—Y in FIGS. 3 and 4, as indicated in FIGS. 3(d) and 4(d), the fuelgas is surrounded by the seal material 3 so as to enter from the fuelgas inlet aperture 45 located on the upper side in these figures, and isguided to the fuel gas outlet aperture 46 located on the lower sidetherein.

In other words, the power generation films 2 a and 2 b have twodifferent configurations in which the structure concerning the fuel gasflow passages 42 is the same, whereas the air flow passages 41 aresymmetric with respect to the axis of fuel gas flow.

The power generation films 2 a, 2 b having two such different structuresare so arranged to constitute a unified cell structure 12 (hereinafterstack 12), wherein from top to bottom an interconnector 1, a powergeneration film 2 a, an interconnector 1, a power generation film 2 b,etc., are alternately superposed upon one another, thus forming multiplelayers with interconnectors and power generation films being sandwichedalternately, and the power generation films being stacked in analternating sequence of 2 a, 2 b, 2 a, 2 b . . . .

FIG. 5 is a perspective view exemplifying a SOFC according to thepresent invention, wherein the stack 12 thus constituted is placedvertically and is provided with manifolds for gas supply and discharge.

In the said figure, reference numerals 53 a, 53 b denote air inletmanifolds; 54 a, 54 b, air outlet manifolds; 55, a fuel gas inletmanifold; 56, a fuel gas outlet manifold.

The air inlet manifold 53 a is attached so that about a half of thetotal inlet air volume is provided to the oxygen electrode side of eachpower generation film 2 a, whereas the air outlet manifold 54 a isfitted so that all the air that has passed the power generation films 2a can be discharged.

In a similar manner, the air inlet manifold 53 b and the air outletmanifold 54 b are attached so that about the remaining half of the totalinlet air volume is provided to, and discharged from the oxygenelectrode side of each power generation film 2 b.

On the other hand, the fuel gas inlet manifold 55 is fitted so that thewhole inlet fuel gas can be supplied to the fuel electrode side of allthe power generation films 2 a and 2 b, whereas the fuel gas outletmanifold 56 is attached so that the whole fuel gas after the cellreaction can be discharged.

Reference numeral 71 in FIG. 5 denotes a current collector plate; 72 and73, current collector bars and current collector parts, respectively.

FIG. 6 is a perspective view illustrating a SOFC in which the stack 12shown in FIG. 1 is placed horizontally, wherein the numerals refer tothe same components as in FIG. 5.

In the horizontally placed SOFC shown in FIG. 6, the fuel gas inletmanifold 55 is fitted on the lower side of the horizontally placed stack12, and the fuel gas outlet manifold 56 on the upper side thereof,whereas the air inlet manifolds 53 a, 53 b are fitted in about thatlower half of the side of the horizontally placed stack 12 which iscloser to the fuel gas inlet manifold 55, and the air outlet manifolds54 a, 54 b are fitted in about that upper half of the side of the stack12 which is closer to the fuel gas outlet manifold 56.

In order to generate power in a SOFC of the present invention, thetemperature is kept at 800° C.˜1000° C. as in conventional SOFC'S, andan oxidant gas (e.g. air, hereinafter air) and a fuel gas are providedto flow in their respective flow passages. In the SOFC in which thepower generation films 2 a are so constituted as in FIGS. 1, 2, 3, 5,and 6, air is supplied from the air inlet manifold 53 a, passing throughthe air inlet aperture 43 a, and after a heat generating reaction in theeffective power generation area which constitutes both electrodes ofeach power generation film 2 a, the remaining air (hereinafter exhaustair) is guided through the air outlet aperture 44 a and discharged tothe air outlet manifold 54 a.

Then, in the SOFC in which the power generation films 2 b are soconstituted as in FIGS. 1, 2, 4, 5, and 6 of the present invention, airis supplied from the air inlet manifold 53 b, passing through the airinlet aperture 43 b, and after a heat generating reaction in theeffective power generation area which constitutes both electrodes ofeach power generation film 2 b, the exhaust air is guided through theair outlet aperture 44 b and discharged to the air outlet manifold 54 b.

The fuel gas, on the other hand, is supplied from the fuel gas inletmanifold 55, passing through the fuel gas inlet aperture 45, and after aheat generating reaction in the effective reaction area of the powergeneration films 2 a and 2 b, the exhaust fuel gas is guided through thefuel gas outlet aperture 46 and discharged to the fuel gas outletmanifold 56.

The above-mentioned reaction generates heat so that the temperature nearthe gas supply area is lower than that in the gas outlet area. Thetemperature distribution varies depending on the electrodecharacteristics, the inlet temperature of each gas, and the gas volume.FIG. 19(a) shows, as an example, an isothermal diagram of the unit cellof the power generation film 2 a. The % values in the figure indicateratios when the temperature difference between the gas inlet and the gasoutlet is assumed to be 100%. Even if the temperature difference varieswhen the gas conditions, etc., change, the isothermal diagram remainsalmost the same.

In the power generation film 2 b, the fuel gas flow is in the samedirection as in the power generation film 2 a, and the air flow issymmetric with respect to the axis of fuel gas flow in the powergeneration film 2 a. As a result, an isothermal diagram as shown in FIG.19(b) is obtained.

These isothermal diagrams in FIGS. 19(a), 19(b) are more similar to thatby the parallel method as shown in FIG. 20(b) as compared with theisothermal diagram of the cross flow type given in FIG. 20(a), thuslowering thermal stress and preventing deterioration of the fuel cellperformance which may be caused by shear or separation of the electricalconnection or sealing between the power generation films and theinterconnectors. Besides, reliable characteristics of the cell can alsobe ensured, because cracks between the power generation films and theinterconnectors as well as other similar problems due to excessive localthermal stress can be avoided.

In summary, in a SOFC which comprises either the power generation film 2a or the power generation film 2 b of the present invention, theaforementioned problems associated with the cross flow method and theco-flow method can be solved at the same time, and the advantages ofboth methods can be realized.

Furthermore, in the power generation films 2 a and 2 b of the presentinvention, the isothermal diagrams in FIGS. 19(a) and 19(b) aresymmetric with respect to the direction of fuel gas flow, as far as thegas is supplied to the power generation films under the same condition.As a result, in the SOFC comprising the stack 12 in which the powergeneration films 2 a and 2 b are superposed alternately withinterconnectors sandwiched in-between as in FIGS. 1, 5 and 6, heatexchange in the height direction (i.e. perpendicular to the layers ofthe stack) is promoted, resulting in a uniform temperature distributionthroughout the stack 12.

In other words, in the FOSC in which the layers are so superposed as inFIGS. 1, 5 and 6, an isothermal diagram as shown in FIG. 19(c) isobtained, which is more similar to that in FIG. 20(b) than to thosegiven in FIGS. 19(a) and 19(b). Therefore, the heat stress in this caseis almost equal to that of the parallel flow method, and is smaller thanin the SOFC in which only one of the power generation films 2 a or 2 bis used. As a result, reliable characteristics of the cell can beensured.

In the present invention, it is desirable to incorporate eachinterconnector 1 in a thin and flat shape as shown in FIG. 1, becausemore heat exchange in the direction perpendicular to the layers lowersthermal stress and enhances the characteristics of the fuel cell. One ofthe means to promote such heat exchange is, for example, to providegrooves in the interconnectors, which increase the surface area thatcomes in direct contact with the gases, and significantly decrease thethermal stress in the present invention.

In contrast to the SOFC according to the conventional co-flow methodshown in FIG. 21, a SOFC according to the present invention does notrequire a header 5, which does not contribute to power generation, inorder to rectify the gas flow, and can provide oxygen electrodes andfuel gas electrodes over a wide range of solid eletrolytes, thusincreasing the effective area that can be used for power generation.

This means that the area for the header 5 can be used as part of theeffective power generation area, and as a result, the effective powergeneration area of the embodiment of the invention shown in FIG. 2 is10%˜25% larger than that of a SOFC by the conventional co-flow methodwhich needs a header shown in FIG. 21. In other words, in order toobtain the same power output in the present invention as in theconventional SOFC, only 80%˜90% of the amount of unit cells of theconventional fuel cells are required.

As shown in the perspective views in FIGS. 5 and 6, even if manifoldsand current collector parts are fitted to the SOFC of the invention,sufficient compactness can be ensured, thus providing a highlyeconomical SOFC.

In the horizontally placed SOFC of the present invention as shown inFIG. 6, the gas inlet aperture (43 a, 43 b, 45 in FIG. 1) which is in alower temperature range is arranged on the lower side of thehorizontally placed stack 12, and the gas outlet aperture (44 a, 44 b,46 in FIG. 1) which is in a higher temperature range due to the heatgenerating cell reaction is on the upper side of the horizontally placedstack 12. In such an arrangement, about a half of the total inlet airvolume is supplied from the air inlet manifold 53 a to the oxygenelectrode side of the power generation film 2 a, and after beinggradually heated up by the cell reaction of the power generation film 2a, discharged to the air outlet manifold 54 a. Similarly, about theremaining half of the total inlet air volume is supplied from the airinlet manifold 53 b to the oxygen electrode side of the power generationfilm 2 b, and after being gradually heated up by the cell reaction,discharged to the air outlet manifold 54 b. The fuel gas, on the otherhand, is supplied from the fuel gas inlet manifold 55 to the fuel gaselectrode side of the power generation films 2 a, 2 b, and after beinggradually heated up by the cell reaction, discharged to the fuel gasoutlet manifold 56.

In the horizontally placed SOFC shown in FIG. 6 of the invention, thegas flow passage is so constituted that the air and the fuel gas areguided from the lower to the upper part, then being heated by the cellreaction, resulting in buoyancy due to a reduced specific weight, whichmakes the gas flow from the lower to the upper part smoother than in avertically placed SOFC such as in FIG. 1.

Therefore, in the horizontally placed SOFC in FIG. 6, the temperaturedifference between the gas inlet aperture and the gas outlet aperture inthe cell becomes smaller than that in the vertically placed SOFC shownin FIG. 5, thus limiting the heat stress to provide a SOFC which is notonly highly reliable, but also economical as the energy required for gassupply can be kept at a low level.

As described above, in a SOFC according to the present invention, thetemperature distribution in the stack due to the heat generation by thecell reaction can be similar to that of a FOSC according to the co-flowmethod, and the heat stress can be made smaller than that of a SOFC bythe cross flow method, thus making it possible to reduce damages in theelectrical connection between the power generation films and theinterconnectors or in the sealing part, as well as cracks and otherproblems in the power generation films or in the interconnectors. As aresult, a highly reliable SOFC can be provided.

In addition, a SOFC of -he present invention does not require a gas flowrectifying section (where no power is generated) which is one of thedisadvantages of the co-flow method, and can ensure an effective powergeneration area which is comparable with that by the cross flow method,thus providing a compact and economical SOFC.

In summary, the present invention provides a SOFC that compensates thedisadvantages of the cross flow method and of the co-flow method, andrealizes the advantages of both methods at the same time.

In the above explanation referring to FIGS. 1, 2, 3, 4, and 5, the upperside of the power generation films is the oxygen electrode and the lowerside thereof is the fuel electrode. However, the upper side and thelower side may be reversed.

It is also possible to replace the oxygen electrode side and the fuelelectrode side completely with each other to realize a SOFC whichcomprises two kinds of fuel gas passages and one kind of air flowpassage, with an effect provided by the present invention.

In the embodiments described above, a configuration in which powergeneration films are superposed via interconnectors comprising groovesas in FIG. 1, and another configuration in which power generation filmscomprise dimples all over the surface thereof as in FIG. 2 areexemplified. However, it goes without saying that the present inventionis not limited to such embodiments, and can be applied to any form offuel cell.

[Embodiment 2]

FIG. 7 is an exploded perspective view showing a planar type solid oxideelectrolyte fuel cell (hereinafter SOFC) according to the secondembodiment of the invention; FIG. 8(a), a sectional view taken alongline X—X in F-G. 7; FIG. 8(b), a sectional view taken along line Y—Y inFIG. 7. FIGS. 9 and 10 are schematic views of intermediateinterconnectors according to the second embodiment, illustrating twodifferent groove patterns as air flow passages.

The second embodiment is an example in which the present invention isapplied to a typical planar SOFC by the cross flow method as shown inFIGS. 17, 18(a), and 18(b).

The planar SOFC according to the second embodiment of the invention willbe described with reference to the exploded perspective view in FIG. 7,the sectional view shown in FIG. 8(a) taken along line X—X, and FIG.8(b) along line Y—Y in FIG. 7, respectively, as well as the schematicviews in FIGS. 9 and 10.

Reference numeral 2 in FIGS. 7, 8(a), and 8(b) denotes a powergeneration film. Each power generation film 2 is composed of a planarsolid electrolyte film 20 which comprises an oxygen electrode 23 on oneside and a fuel electrode 24 on the other side thereof. In the drawing,the upper side of the power generation film 2 is the fuel electrode 24and the lower side the oxygen electrode 23. Reference numerals 1 a, 1 b,1 c, and 1 d in the drawing refer to the interconnectors which aresuperposed alternately with power generation films 2 to form a unifiedcell structure 13 (hereinafter stack 13).

FIGS. 9 and 10 are schematic views of interconnectors 1 a, 1 b,respectively. The interconnectors 1 a and 1 b are those which are placedin the intermediate layers of the stack 13 as shown in FIG. 7, bothsides of which are surrounded by the support frame 31 of the powergeneration films, except the gas inlet aperture and the gas outletaperture where the gases pass. The support frame 31 and thecircumference of the power generation films 2 contact tightly with thesandwiched seal material 3, thus securing tightness for the gases thatflow through the inside of the cell.

On both sides of the interconnectors 1 a and 1 b, multiple island-shapedprotrusions 32 are arranged in an orderly manner to constitute multiplerows of gas flow grooves 33. The top of the island-shaped protrusions 32contacts or connects with the fuel electrode 24 or the oxygen electrode23, thus supporting the power generation films 2 as well as connectingthe adjacent power generation films electrically in series. As shown inFIGS. 9 and 10, the interconnectors 1 a and 1 b are different concerningthe shape of the air flow passage 41 which contacts the fuel electrodeside of the adjacent power generation film, and are the same concerningthe shape of the gas flow passage 42 which contacts the fuel electrodeside of the adjacent power generation film.

Reference numerals 43 a and 43 b in FIGS. 9 and 10 denote air inletapertures; 44 a and 44 b, air outlet apertures; 45, a fuel gas inletaperture; 46, a fuel gas outlet aperture. The fuel gas inlet aperture 45is open along the whole length of one side of the rectangularinterconnector, and the gas outlet aperture 46 is open along the wholelength of the side opposite to the side which is provided with the fuelinlet aperture 45.

The air inlet apertures 43 a, 43 b and the air outlet apertures 44 a, 44b are placed on the back side (the side which contacts the air electrode23 of the power generation film) of the remaining two sides of therectangular interconnector, the said two sides having neither the fuelgas inlet aperture 45 nor the fuel gas outlet aperture 46. The air inletapertures 43 a, 43 b are provided in about that half of the said sidewhich is closer to the fuel gas inlet aperture 45, and the air outletapertures 44 a, 44 b in about that half of the said side which is closerto the gas outlet aperture 46.

In the interconnector 1 a shown in FIG. 9, the air flow passage 41 isconstituted on the surface of the interconnector so that the air entersthrough the air inlet aperture 43 a which is located in the lower rightpart and is guided to the air outlet aperture 44 a in the upper leftpart in FIG. 9(a).

In the interconnector 1 b shown in FIG. 10, the air flow passage 41 isconstituted so that the air enters through the air inlet aperture 43 bwhich is located in the lower left part and is guided to the air outletaperture 44 b in the upper right part in FIG. 10(a).

The fuel gas flow passages 42, on the other hand, have the same shape inboth interconnectors 1 a and 1 b. As shown in FIGS. 9(d) and 10(d), asupport frame 31 for the adjacent power generation film is provided inthe circumference, and the fuel gas flow passages 42 are constituted inthe middle part of the interconnector surface, so that the fuel gasenters through the fuel gas inlet aperture 45, and is guided to the fuelgas outlet aperture.

As explained above, the interconnectors 1 a, 1 b are two differentstructures in which the fuel gas flow passages 42 have the same shape,and the air flow passages 41 are symmetric with respect to the directionof the fuel gas flow.

The interconnector 1 c in FIG. 7 is an upper interconector placed on topof the stack 13, the upper surface of which is usually flat to fitcurrent collector parts, and the lower surface of which has the sameshape as the lower surface of the interconnector 1 a or 1 b (FIG. 9(d)or FIG. 10(d)) described earlier, corresponding to the fuel electrodeside of the adjacent power generation film 2. The interconnector Id is alower interconnector placed in the lower end of the stack 13, the uppersurface of which has the same shape as the upper surface of theinterconnector 1 a or 1 b (FIG. 9(a) or FIG. 10(a)), corresponding tothe oxygen electrode side of the adjacent power generation film 2,whereas the lower surface thereof is usually flat to fit currentcollector parts.

The interconnectors 1 a, 1 b, 1 c, 1 d and the power generation films 2having the above features are then superposed alternately as shown inFIG. 7, wherein, from top to bottom, an interconnector 1 a, a powergeneration film 2, an interconnector 1 b, . . . , a power generationfilm 2, an interconnector 1 d are alternately superposed, whereas theinterconnectors except the uppermost and lowermost interconnectors 1 c,1 d constitute a unified structure (stack 13) in such a manner that theinterconnectors 1 a, 1 b, 1 a, 1 b, . . . are superposed alternately.

Compared with the stack 12 in the first embodiment, the stack 13 thusconstituted is the same as the first embodiment of the present inventionconcerning the basic structure and functions, except that the inlet andoutlet apertures as well as the flow passages are constituteddifferently. Therefore, the SOFC of the second embodiment which isequipped with manifolds to supply and discharge gases can be regarded asthe SOFC having the same appearance and functions as in the SOFC shownin FIG. 5. Also, similar to the first embodiment explained withreference to FIG. 6, the stack 13 can be placed horizontally with thefuel outlet aperture 46 toward upwards and the fuel inlet aperture 45toward downwards.

When compared with the stack 12 in the first embodiment of theinvention, the stack 13 constituted as in FIG. 7 has the same basicstructure and functions in terms of gas supply and discharge, exceptthat the gas flow passages which are sandwiched between theinterconnectors and the power generation films are constituteddifferently, thus reducing the heat stress in a manner similar to thefirst embodiment, and providing a highly reliable SOFC as a result.

Also in the second embodiment, similar to the first embodiment, it ispossible to increase the surface area of the interconnectors that comein contact with gases to promote heat exchange and reach an effectintended by the present invention. For this reason, it is preferable toincrease the number of grooves for gas flow on the surface of theinterconnectors to obtain the largest possible contact surface withgases. In the stack 13 in the second embodiment of the invention,similar to the stack 12 of the first embodiment, it is possible to adoptthe configuration shown in FIGS. 5 and 6 in order to have comparablefunctions and effects, thus providing a highly reliable and economicalSOFC.

In FIGS. 7, 8(a), 8(b), 9(a), (b), (c), (d), 10(a), (b), (c), (d)explained above, the upper side of the power generation films is thefuel electrode, and the lower side thereof the oxygen electrode.However, the oxygen electrode side and the fuel electrode side may bereversed. A comparable effect can also be obtained by replacing theoxygen electrode side and the fuel electrode side completely toconstitute a SOFC having two kinds of fuel gas flow passages and onekind of air flow passage, thus realizing another SOFC according to thesecond embodiment of the invention.

In the second embodiment of the invention, an example in which theinterconnectors are provided with grooves to form gas passages is shown.However, as explained in the first embodiment, as far as gas passagescan be constituted between the interconnectors and the power generationfilms to provide gases to both electrodes of the power generation filmsand electrical connections (contact or connection between theinterconnectors and the power generation films) can be provided, anyconfiguration can constitute a SOFC of the present invention to obtainsimilar effects.

[Embodiment 3]

FIG. 11 is an exploded perspective view showing a planar type solidelectrolyte fuel cell (hereinafter SOFC) according to the thirdembodiment of the invention; FIG. 12, a sectional view taken along lineX—X in FIG. 11; FIGS. 13 and 14, each showing a side view and sectionalviews to illustrate two types of unit cells with internal manifolds, inwhich different kinds of air flow passages are realized.

In FIGS. 5 and 6, an example is shown in which manifolds for gas supplyand discharge are attached to the outside of the stack 12 according tothe first embodiment of the invention. This type of gas supply anddischarge is generally called an external manifold type. On the otherhand, there is a SOFC called an internal manifold type in which thestack comprises the said manifold function. In this case, through-holesare provided in the interconnectors and the power generation films as ameans to cause gases to flow in the direction perpendicular to thesuperposed layers, and the interconnectors and the power generationfilms are superposed alternately to form a unified structure in which aspace having the same function as manifolds is formed inside the stack.

To explain a SOFC according to the third embodiment, an example will behereunder described in which the present invention is applied to theabove-mentioned SOFC of the internal manifold type.

FIGS. 13 and 14 are schematic views showing unit cells according to thethird embodiment of the invention, corresponding to the schematic viewsof the unit cells of the external manifold type as explained in FIGS. 3and 4 in the first embodiment. Reference numerals in FIGS. 13, 14correspond to those in FIGS. 3 and 4, and their basic structures andfunctions are the same.

On the fuel electrode side of one of the four sides of the rectangularpower generation films 2 a and 2 b, a fuel inlet aperture 45 is providedover nearly the entire length thereof, whereas on the air electrode sideof one of the remaining two sides air inlet apertures 43 a, 43 b areprovided in about that half of the said side which is closer to the fuelinlet aperture, and air outlet apertures 44 a, 44 b are provided inabout that half of the side which is closer to the fuel gas outletaperture, the said side facing the side with the air outlet apertures 43a, 43 b.

The difference between this embodiment and the first embodiment in FIGS.3 and 4 is that six through-holes are provided in the interconnectors 1and the power generation films 2 a, 2 b. Reference numerals 61 a and 61b in FIGS. 13 and 14 denote air supply holes; 62 a and 62 b, air outletholes; 63, a fuel inlet hole; 64, a fuel gas outlet holes.

In the power generation film 2 a shown in FIG. 13, the air supply hole61 a and the air inlet aperture 43 a are connected with each other onthe oxygen electrode side, whereas the air outlet hole 62 a and the airoutlet aperture 44 a are connected with each other. The circumference ofthe other through-holes 61 b, 62 b, 63, and 64 is surrounded andinsulated by the seal material 3, so that no gas can invade the oxygenelectrode 23 of the power generation film 2 a.

The air which is supplied from the air supply hole 61 a to the air inletaperture 43 a is surrounded by the seal material 3 so as to pass theoxygen electrode surface 23, going through the air outlet aperture 44 a,and is discharged to the air outlet hole 62 a. Similarly, in the powergeneration film 2 b shown in FIG. 14, the air which is supplied from theair supply hole 61 b to the air inlet aperture 43 b is surrounded by theseal material 3 so as to pass the oxygen electrode surface 23, goingthrough the air outlet aperture 44 b, and is discharged to the airoutlet hole 62 b.

The interconnectors and the power generation films comprising the abovefeatures are superposed alternately to form a unified fuel cell 14(hereinafter stack 14), wherein the power generation films are alsosuperposed alternately in a sequence 2 a, 2 b, 2 a, 2 b, etc.

In the stack 14 thus constituted, through-holes provided in eachinterconnector and each power generation film are superposed in thedirection perpendicular to the layers to form manifolds inside thestack. In such a manner, a SOFC which is equivalent to the SOFC of theextrernal manifold type in the first embodiment in FIG. 5 in terms ofstructure and functions is realized. Also, in a horizontal arrangementin which the fuel gas outlet aperture 46 in the stack 14 of the thirdembodiment is placed toward an upward direction and the fuel gas inletaperture 45 toward a downward direction, a SOFC equivalent in terms ofstructure and functions to the SOFC of the external manifold type shownin FIG. 6 can be realized.

The stack 14 in the SOFC of the internal manifold type which isconstituted by superposing the interconnectors and the power generationfilms shown in FIG. 11 alternately is equivalent in terms of structureand functions to the SOFC shown in FIGS. 3 and 6 in which manifolds areprovided externally as in the first embodiment of the invention. As aresult, an effect similar to that explained in the first embodiment canbe obtained in the third embodiment as well, thus providing a compactand economical SOFC.

In the third embodiment of the invention as in FIGS. 11, 12, 13, and 14,the upper surface of the power generation films 2 a, 2 b are the oxygenelectrode, and the lower surface thereof the fuel electrode. However,the upper side and the lower side may be reversed. Also, in a SOFC ofthe internal manifold type constituted by replacing the oxygen electrodeside and the fuel electrode side completely to comprise two kinds of gasfuel passages and one kind of air passage, an effect similar to thatexplained in the first embodiment can be obtained, as an example of thethird embodiment of the invention.

Furthermore, in the interconnectors and the power generation films shownin FIGS. 7, 8(a), 8(b), 9(a), (b), (c), (d), and 10, similar to themanner explained in FIG. 11, a stack of the internal manifold typehaving a structure and a function equivalent to that of a SOFC of theinvention can be obtained by providing 6 through-holes in thecircumference. It is also possible to use the ascending flow caused bythe buoyancy of the heated gas by the horizontal arrangement in whichthe fuel gas outlet aperture faces upwards, thus incorporating excellentreliability and economy. In the third embodiment of the invention, anexample is shown in which internal manifolds are applied to all the gasinlet and outlet apertures in 6 positions. However, if some of these areof the external manifold type, for example, the fuel gas side is of theexternal manifold type and the air side is of the internal manifoldtype, functions and effects of the present invention can be ensured byproviding the interconnectors and the power generation films with airinlet and outlet through-holes in 4 positions, and superposing themalternately, etc.

[Embodiment 4]

FIG. 23 is a simplified drawing of a planar type solid electrolyte fuelcell (SOFC) according to the fourth embodiment of the invention. FIG.24(a) is a sectional view of the major part of an air chamber of thefourth embodiment. FIG. 24(b) is a sectional view of another air chamberof the fourth embodiment.

This embodiment is a variation of the horizontally placed fuel cell inthe first embodiment shown in FIG. 6, wherein a substack as a unit iscomposed of multiple rows of vertically arranged power generation filmswith interconnectors sandwiched in-between, and ten such substacks 101are connected like a freight train using intermediate current collectorparts to form a horizontally placed stack train 102, thus constituting ahorizontally placed SOFC.

The first substack and the tenth substack at both ends of thehorizontally placed stack train 102 are with equipped each a currentcollector plate 109 comprising a current collector bar 108 in order tocollect current. The horizontally placed stack train 102 is contained ina fuel cell chamber which is not shown in the drawing in a state inwhich the current collector bars 108 are pressurized from both ends.

In the present embodiment, the current collector part which is not shownin the drawing comprises lead wires 110 for current bypass in FIG. 23.For the lead wires 110, cables which are composed of nickel wires orplates can be used. Even if lead wires 110 are used, there is no dangerof the said lead wires being oxidized, because the inside of thesubstack containers is situated lower than the environment in whichreduction by fuel outlet gases can occur.

The lead wires 110 can be used to measure the voltage of the substacksconstantly so that a bypass circuit can be formed as soon as any of thesubstacks fails, thus making it possible to prevent the other substacksthat still function properly from being deteriorated, and improve thereliability of the cell operation.

In this horizontally placed fuel cell, each substack comprises a gassupply chamber. In FIG. 23, air chambers are provided on both sides, andfuel chambers are placed on the lower side of the stack, so that the gasis supplied from the lower part to the upper part. In the presentembodiment, the fuel chambers are omitted in the drawing.

In each of the above substacks 101, a multiple number of (e.g. ten)power generation films are connected with interconnectors sandwichedin-between, and, for example, ten such substacks are placed in a row toform a fuel cell. In the present embodiment, the air flow of the first,third, fifth, seventh and ninth substacks and the air flow of thesecond, fourth, sixth, eighth and tenth substacks are exchanged witheach other on a substack basis.

The air flow of the substacks on the air electrode side is illustratedin FIG. 24. FIG. 24(a) shows the air flow of the first, third, fifth,seventh and ninth substacks, and FIG. 24(b) the air flow of the second,fourth, sixth, eighth and tenth substacks in FIG. 23, respectively.

In the case illustrated in FIG. 24(a), the air from the air inlet pipe112 is introduced inside from the air inlet aperture 111 a having anopening provided in about the lower half of the right side in thedrawing, and the air thus introduced is gradually warmed by the cellreaction and flows up diagonally upwards along the air electrode surfaceof the power generation film 113, whereas the exhaust air is dischargedfrom the air outlet aperture 114 a having an opening in about the upperhalf of the left side of the drawing and through the air outlet pipe115. The fuel gas, on the other hand, is supplied from the fuelcombustion chamber 116 placed in the lower part of the stack.

In the case shown in FIG. 24(b), the air from the air inlet pipe 112 isintroduced inside from the air inlet aperture 111 a having an opening inabout the lower half of the left side in the drawing, and the air thusintroduced is gradually warmed by the cell reaction and flows updiagonally upwards along the air electrode surface of the powergeneration film 113, whereas the exhaust air is discharged from the airoutlet aperture 114 a having an opening in about the upper half of theright side in the drawing and through the air outlet pipe 115. The fuelgas, on the other hand, is supplied from the fuel chamber 116 placed inthe lower part of the stack.

Although the temperature distribution is asymmetric in each individualsubstack as shown in FIG. 19, substacks having opposite air supplydirections can be combined with each other to realize a uniformtemperature distribution in the fuel cell as a whole, and as a result,the heat stress is comparable with that of a co-flow type, thus ensuringreliable cell characteristics.

In summary, in the horizontally placed fuel cell in FIG. 23, similar tothe horizontally placed fuel cell of the present invention shown in FIG.6, the gas flow passages are so constituted that the air and the gas areguided from bottom to top, being warmed by the heat generated by thecell reaction, wherein the air and the gas thus heated decrease inspecific weight and cause buoyancy which makes the gas flow from bottomto top smoother as compared with the vertically placed arrangement shownin FIG. 1.

This means that also the horizontally placed SOFC in FIG. 23, ascompared with the vertically placed SOFC of the laminated type shown inFIG. 5, the temperature difference between the gas inlet aperture andthe outlet aperture in the cell can be decreased, thereby reducing theheat stress, thus providing a highly reliable SOFC, while keeping theenergy required for gas supply at a low level to offer an economicalSOFC.

In the substacks in FIG. 23 described above, the air is suppliedalternately in each individual stack. However, it is also possible tointroduce the air alternately in each individual power generation filmwithin one substack, so as to realize amore uniform temperaturedistribution.

FIG. 25 illustrates an example in which the air is introducedalternately to the air electrodes in each individual substack.

In the example shown in FIG. 25(a), four power generation films arealternately sandwiched via interconnectors 1, whereas unified air supplychambers are provided on both sides to constitute a stack 201.

The air chambers 202 on both sides are each divided into the upper andthe lower chamber by the separation wall 203, wherein the air supplypipe 204 is connected to the lower chamber 205 and the air outlet pipe206 connected to the upper air chamber 207, and the air inlet apertures205 a having an opening about half the size of the fuel supply side areplaced alternately in a row to supply air alternately from the left andfrom the right, whereas the air is discharged alternately through theoutlet apertures 207 a which are located diagonally upper left to theair inlet apertures and have each an opening of about half the fueloutlet side, so that the temperature distribution becomes uniform withineach individual stack, thus activating the cell reaction. In this case,the heat of the discharged air can be used to warm the supplied airwithout any special equipment because the air is supplied and dischargedthrough double pipes, thus adding the function of a heat exchangereasily to the part of the embodiment. Similarly, in an embodiment inwhich the fuel is supplied and discharged through double pipes, theoxygen electrode side and the fuel electrode side can be replacedcompletely with each other to add the function of a heat exchangereasily, wherein it is also possible to realize a gas reforming functionreadily and at a low cost in a limited space by providing a catalystlayer in the gas supply pipes, if, for example, town gas is used as thefuel for cells.

As explained above, the air chambers that serve as manifolds for airsupply can be made smaller by limiting the number of power generationfilms which constitute the substacks. Furthermore, by connecting aplurality of such substacks, a uniform temperature distribution in thewhole fuel cell can be realized, thus limiting the heat stress to thelevel which is equivalent or superior to that by the co-flow method,ensuring reliable cell characteristics.

In contrast to the cases in which several dozens of stacks are placednext to or upon one another, manifolds and other components according tothe present invention need not be large-sized, thus improving thesealing capability as well as reducing the manufacturing cost of thefuel cells.

INDUSTRIAL APPLICABILITY

As described above, the present invention provides a compact andeconomical solid electrolyte fuel cell in which the generated heatstress is small to ensure reliable characteristics of the fuel cell andthe structure is simple as by the cross flow method to provide a widepower generation area.

What is claimed is:
 1. A solid oxide electrolyte fuel cell, comprising:a planar power generation film including a solid electrolyte layer, anoxygen electrode formed on a first surface of the solid electrolytelayer, and a fuel electrode formed on a second surface of the solidelectrolyte layer, said film having a pair of first opposing sides and apair of second opposing sides substantially perpendicular to the firstopposing sides; a first interconnector facing the fuel electrode andforming a first space between one side the first interconnector and thefuel electrode; a second interconnector facing the oxygen electrode andforming a second space between one side of the second interconnector andthe oxygen electrode; a fuel gas inlet aperture for supplying fuel gasinto the first space, the fuel gas inlet aperture being provided in avicinity of the one of the first opposing sides of the power generationfilm between the first interconnector and the fuel electrodesubstantially along an entire length of the one of first opposing sides;a fuel gas outlet aperture for exhausting the fuel gas from the firstspace, the fuel gas outlet aperture being provided in a vicinity ofanother of the first opposing sides of the power generation film betweenthe first interconnector and the fuel electrode substantially along anentire length of the another of the first opposing sides; an air inletaperture for providing oxidant gas into the second space, the air inletaperture being provided in a vicinity of the one of the second opposingsides of the power generation film between the second interconnector andthe oxygen electrode and having about half a length of one of the secondopposing sides at a position adjacent the fuel gas inlet aperture; andan air outlet aperture for exhausting the oxidant gas from the secondspace, the air outlet aperture being provided in a vicinity of anotherof the second opposing sides of the power generation film between thesecond interconnector and the oxygen electrode and having about half alength of the another of the second opposing sides at a positionadjacent the first fuel outlet aperture.
 2. The solid electrolyte fuelcell according to claim 1, wherein said power generation film is a solidelectrolyte including a plurality of dimples.
 3. The solid oxide fuelcell according to claim 1, further comprising: a first seal materialprovided between the peripheral portion of the power generation filmbetween the first interconnector and the fuel electrode, and defines thegas fuel inlet aperture and the gas fuel outlet aperture; and a secondseal material provided between the peripheral portion of the powergeneration film between the second interconnector and the air electrode,and defines the air inlet aperture and the air outlet aperture.
 4. Thesolid electrolyte fuel cell according to claim 1, wherein said firstinterconnector includes a first circumferential wall protruding towardsthe power generation film and defining the gas fuel inlet aperture andthe gas fuel outlet aperture, and said second interconnector includes asecond circumferential wall protruding towards the power generation filmand defining the air inlet aperture and the air outlet aperture.
 5. Thesolid electrolyte fuel cell according to claim 4, wherein said firstinterconnector includes a plurality of first protrusions forming aplurality of grooves in the one side of the first interconnector, andsaid second interconnector includes a plurality of second protrusionsforming a plurality of second grooves in the one side of the secondinterconnector.
 6. The solid electrolyte fuel cell according to claim 1,wherein the solid electrolyte fuel cell is placed such that said gasinlet aperture is lower than said gas outlet aperture.
 7. The solidelectrolyte fuel cell according to claim 1, wherein at least one of saidair inlet aperture, said air outlet aperture, said fuel gas inletaperture, and said fuel gas outlet aperture is a manifold provided inthe planar power generation film.
 8. A solid oxide electrolyte fuelcell, comprising: a first cell having a pair of first opposing sides anda pair of second opposing sides substantially perpendicular to the firstopposing sides, said first cell including, a first planar powergeneration film including a first solid electrolyte layer, a first fuelelectrode formed on a first surface of the first solid electrolytelayer, and a first air electrode formed on a second surface of the firstsolid electrolyte layer, a first interconnector facing the first fuelelectrode and forming a first space between one side the first interconnector and the first fuel electrode, a first fuel gas inlet aperturefor supplying fuel gas into the first space, the first fuel gas inletaperture being provided in a vicinity of the one of the first opposingsides of the first cell between the first interconnector and the firstfuel electrode substantially along an entire length of the one of firstopposing sides, a first fuel gas outlet aperture for exhausting the fuelgas from the first space, the first fuel gas outlet aperture beingprovided in a vicinity of another of the first opposing sides of thefirst cell between the first interconnector and the first fuel electrodesubstantially along an entire length of the another of the firstopposing sides, a second interconnector facing the first air electrodeand forming a second space between one side of the second interconnectorand the first air electrode, a first air inlet aperture for providingoxidant gas into the second space, the first air inlet aperture beingprovided in a vicinity of the one of the second opposing sides of thefirst cell between the second interconnector and the first oxygenelectrode and having about half a length of the one of the secondopposing sides at a position adjacent the first fuel gas inlet aperture,a first air outlet aperture for exhausting the oxidant gas from thesecond space, the first air outlet aperture being provided in a vicinityof the another of the second opposing sides of the first cell betweenthe second interconnector and the first oxygen electrode and havingabout half a length of the another of the second opposing sides adjacentthe first fuel outlet aperture; and, a second cell provided adjacent thefirst cell and having the pair of first opposing sides and the pair ofsecond opposing, said second cell including, a second planar powergeneration film including a second solid electrolyte layer, a secondoxygen electrode formed on a first surface of the second solidelectrolyte layer, and a second fuel electrode formed on a secondsurface of the second solid electrolyte layer, a third space formedbetween another side of the second interconnector and the second fuelelectrode, a second fuel gas inlet aperture for supplying the fuel gasinto the third space, the second fuel gas inlet aperture being providedin a vicinity of the one of the first opposing sides of the second cellbetween the second interconnector and the second fuel electrodesubstantially along an entire length of the one of first opposing sides,a second fuel gas outlet aperture for exhausting the fuel gas from thethird space, the second fuel gas outlet aperture being provided in avicinity of another of the first opposing sides of the second cellbetween the second interconnector and the second fuel electrodesubstantially along an entire length of the another of the firstopposing sides, a third interconnector facing the second air electrodeand forming a fourth space between one side of the third interconnectorand the second air electrode, a second air inlet aperture for providingthe oxidant gas into the fourth space, the second air inlet aperturebeing provided in a vicinity of the another of the second opposing sidesof the second cell between the third interconnector and the secondoxygen electrode and having about half a length of the another of thesecond opposing sides at a position adjacent the second fuel gas inletaperture, and a second air outlet aperture for exhausting the oxidantgas from the fourth space, the second air outlet aperture being providedin a vicinity of the one of the second opposing sides of the second cellbetween the third interconnector and the second oxygen electrode andhaving about half a length of the one of the second opposing sidesadjacent the second fuel outlet aperture.
 9. The solid electrolyte fuelcell according to claim 8, wherein said first and second powergeneration films are a solid electrolyte including a plurality ofdimples.
 10. The solid electrolyte fuel cell according to claim 8,wherein the first and second cells are placed such that the first andsecond gas inlet apertures are lower than the first and second gasoutlet apertures.
 11. The solid electrolyte fuel cell according to claim8, wherein the solid electrolyte fuel cell includes a plurality of firstand second cells that are stacked together such that the first cells andthe second cells are alternately provided.
 12. The solid electrolytefuel cell according to claim 8, wherein the first and second gas inletapertures are manifolds provided in the first and second planar powergeneration films, respectively.
 13. The solid electrolyte fuel cellaccording to claim 8, wherein the first and second gas outlet aperturesare manifolds provided in the first and second planar power generationfilms, respectively.
 14. A solid oxide electrolyte fuel cell,comprising: a planar power generation film including a first electrodeand a second electrode and second electrodes, said film having a pair offirst opposing sides and a pair of second opposing sides substantiallyperpendicular to the first opposing sides; a first interconnector facingthe first electrode and forming a first space between one side the firstinterconnector and the first electrode; a second interconnector facingthe second electrode and forming a second space between one side of thesecond interconnector and the second electrode; a first gas inletaperture for supplying a first gas into the first space, the first gasinlet aperture being provided in a vicinity of the one of the opposingsides of the power generation film between the first interconnector andthe first electrode substantially along an entire length of the one offirst opposing sides; a first gas outlet aperture for exhausting thefirst gas from the first space, the first gas outlet aperture beingprovided in a vicinity of another of the first opposing sides of thepower generation film between the first interconnector and the firstelectrode substantially along an entire length of the another of thefirst opposing sides; a second gas inlet aperture for providing a secondgas into the second space, the second gas inlet aperture being providedin a vicinity of the one of the second opposing sides of the powergeneration film between the second interconnector and the secondelectrode and having about half a length of one of the second opposingsides at a position adjacent the first gas inlet aperture; and an secondgas outlet aperture for exhausting the second gas from the second space,the second gas outlet aperture being provided in a vicinity of anotherof the second opposing sides of the power generation film between thesecond interconnector and the second electrode and having about half alength of the another of the second opposing sides at a positionadjacent the first gas outlet aperture.